The invention relates to a configuration for sealing off a duct or feed-through gap between a housing wall and a shaft to be set into rotation relative to the housing wall, and a sealing ring surrounding the shaft, being sealed with respect to both the housing wall and the shaft and being displaceable relative to the housing wall but not able to be set into rotation by the shaft.
Such "shaft seals" have manifold uses, especially in cases in which the duct of a shaft passing through the wall of a housing is to be sealed, and in which the housing is intended to enclose some fluid other than air. Such devices are necessary, for instance, for shafts of turbo generators that are cooled with a gas, such as hydrogen. When using the seals, it is unimportant to determine whether the pressure of the fluid to be enclosed in the housing is greater or less than the ambient pressure.
Shaft seals of that type are disclosed in German Published, Non-Prosecuted Application DE 37 23 729 A1 and British Patent No. 760,781, for example. Those documents in particular demonstrate versatile possibilities for further developments of the shaft seals. German Published, Non-Prosecuted Application DE 37 23 729 A1 relates to the configuration of a sealing ring on the housing wall having the duct. That sealing ring is not rotatable relative to the housing wall, yet it is intended to be easily displaceable for the sake of centering. In British Patent No. 760,781, versatile possibilities for supplying sealing and/or lubricating fluid to the gap between the sealing ring, housing wall and shaft are disclosed.
The invention relates to possibilities for monitoring the function of a shaft seal of the above-mentioned type. In many cases, namely in large electrical machines and the like, the shaft rotates relative to the housing wall and the sealing ring at high speed (typically 3000 rpm, for turbo generators). Very high demands must accordingly be made for the slidability of the sealing ring on the shaft, and an especially heavy-duty lubrication must typically be provided. Functional monitoring of the seal is desirable in many cases. Such functional monitoring has already been achieved by measuring the temperature of the regions of the sealing ring immediately adjacent the shaft, using suitable sensors. That measuring method is somewhat sluggish, because of the thermal capacity of the sealing ring. Worsening of the sliding properties cannot be recognized until the sealing ring has eventually heated up markedly, so that damage to the sealing ring and/or shaft can only be recognized after some delay. It is accordingly an object of the invention to provide a configuration for sealing off a duct gap between a housing wall and a shaft, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which furnishes a capability of ascertaining worsening in the sliding between the sealing ring and shaft without considerable time lag, and thus makes it possible to avert material damage by taking precautions.
With the foregoing and other objects in view there is provided, in accordance with the invention, a configuration for sealing off a duct gap between a housing wall and a shaft, comprising a sealing ring surrounding a shaft to be set into rotation relative to a housing wall, the sealing ring being sealed off with respect to the housing wall and the shaft, the sealing ring being displaceable relative to the housing wall and being incapable of being set into rotation by the shaft, at least one spring element to be placed under a mechanical strain by a torque exerted upon the sealing ring by the rotation of the shaft, and means for determining the strain and issuing a report, if the strain deviates substantially from a predeterminable normal value.
Since the torque exerted on the sealing ring by the rotation of the shaft is measured directly according to the invention, immediate recognition of any change in the sliding behavior between the shaft and the sealing ring is possible. The time lag associated with the requirement for a certain accumulation of the thermal energy produced by friction is accordingly absent, and a measurement value that directly describes the sliding behavior of the sealing ring on the shaft is available and can be monitored permanently, not only in order to recognize damage that has already begun but also to discover warning signs heralding damage if operation were to be continued.
In accordance with another feature of the invention, the means for determining the mechanical strain of the spring element include at least one measurement pickup located on the spring element and an evaluation device belonging to and being associated with the pickup for evaluating the signals of the measurement pickup and issuing the report.
Electromechanical sensors which can be connected to appropriate interfaces of typical electronic evaluation devices are particularly possible as the measurement pickups. Advantageously, a plurality of measurement pickups are secured to various points of the spring element and wired to one another in a suitable manner. For instance, four strain gauges may be mounted on the spring element and connected to one another to make a Wheatstone bridge. In this way, influences that are disruptive on the measurement of the mechanical strain, which as can be caused, for instance, by temperature influences, can be suppressed. The accuracy of measurement and thus the reliability of the monitoring can be increased considerably.
In the simplest case, the report is an acoustical or optical signal, which is used to order an operator of an apparatus having the configuration as a component, to stop the shaft. However, in the context of the invention, it is also possible to use the measurement values in a suitable automatic system for regulating the flow of lubricant to the sealing ring.
Therefore, in accordance with a further feature of the invention, there is provided a delivery device for delivering the lubricant being coupled with the means for strain measurement and being regulated by the signals generated there.
In accordance with an added feature of the invention, there is provided a bending bar as the spring element, which can be flexed by the torque exerted upon the sealing ring and is provided with at least one electrical measurement pickup, namely at least one strain gauge, along with an associated electrical evaluation device.
Various possibilities exist for attaching the bending bar. For instance, in accordance with an additional feature of the invention, the bending bar is anchored firmly to the housing wall, and the sealing ring has a protrusion to be pressed against the bending bar by the torque so that the bending bar is bent elastically.
Measurement pickups, such as strain gauges with which the bending can be measured, are mounted on the bending bar in a known manner. Naturally, instead of being provided with a protrusion, the sealing ring may be provided with a slit through which the bending bar is inserted. Furthermore, the bending bar can also be joined to the sealing ring directly, for instance by being screwed into an appropriate bore in the sealing ring extending at right angles to the shaft.
In such a case, in accordance with yet another feature of the invention, there is provided an abutment firmly anchored to the housing wall, against which the bending bar is pressed by the torque. As noted above, the bending bar should be equipped with suitable measurement pickups.
In accordance with yet a further feature of the invention, in any embodiment of the invention with a spring element in the form of a bending bar, the bending bar has a plurality of measurement pickups furnishing complementary signals to determine the bending, the torque always effects the bending of the bending bar in a certain bending direction at a tangent with respect to the rotation, each side of the bending bar defining the bending bar along the bending direction has a measurement pickup, in particular a strain gauge, and during the bending, a compressive strain occurs on one side, while a tensile strain occurs on the other.
This means that the various measurement pickups produce complementary signals, and combining them can increase the accuracy of the strain measurement. Non-linearities in the measuring process can also be suppressed, so that the configuration of a bending bar with two measurement pickups for complementary signals is particularly well suited for inclusion in a closed-loop control device such as the aforementioned regulator for delivering the sealing and/or lubricating fluid to the sealing ring.
Besides the known strain gauges, piezoelectric measurement pickups may also be used as the measurement pickups. In accordance with a concomitant feature of the invention, the measurement pickups are introduced between an abutment being firmly joined to the housing wall and a protrusion of the sealing ring. As a result of the torque, the protrusion presses against the abutment and thus presses on the piezoelectric measurement pickup, producing an electrical voltage that can be measured by conventional means.
Naturally, various types of measurement pickups may be provided. On one hand, this may introduce redundancy into the strain measurement, which may be important for safety reasons, and on the other hand it can increase the accuracy of the measurement process by combining a plurality of measuring methods, optionally with measuring ranges that differ from one another.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a configuration for sealing off a duct gap between a housing wall and a shaft, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.